Radio transmission systems, whether terrestrial radio relay systems or satellite transmission systems, make it possible to install new radio connections, or expand existing ones, very quickly. In such radio transmission systems, the frequency spectrum available should be utilized as optimally as possible. This requirement can be met with point-to-multipoint radio transmission systems (radio relay, satellite radio).
A point-to-multipoint radio relay system is described in "Mikrowellenmagazin" Vol. 10, Number 6, 1984, pp. 629, 630. According to this, publication utilization of the frequency band of the available radio channel can be improved by assigning the necessary frequency band only as necessary. Communication between the central station and the individual subscriber stations takes place either by either frequency-divided multiple access (FDMA) or time-divided multiple access (TDMA), the frequency channels or time slots being apportioned to the subscribers as required.
In a point-to-multipoint radio relay system as described in German Patent Application No. 44 26 183, the transmission capacity is adapted flexibly to subscriber requirements in that the bandwidth of the individual transmission channels is adjusted to the data transmission rate requested in each case by the individual subscribers. Provision is also made for variable setting of the modulation type or modulation depth (for example, n-PSK with n=2 to 16, or M-QAM with M=4 to 256) on the individual transmission channels.
It is the object of the present invention to provide a point-to-multipoint radio transmission system with which transmission capacities can be flexibly allocated and adapted to the on-line subscriber stations without interfering with or interrupting existing radio connections.